Re: [Discuss-gnuradio] USRP FLEX900 Daughter Boards Calibration

[Eric Blossom]

On Wed, Jul 29, 2009 at 04:29:35AM -0700, Shabbir Ahmed wrote:
> 
> Dear All:
> 
> I need to calibrate my USRP with Flex900 daughter boards to take real world
> measurements in dBm. But I am confused with the gain parameter that is used
> in usrp_fft.py.
> 
> 1. Not sure whether the RFX900 board has a PGA of its own

The RFX boards have adjustable gain on the Rx side, controlled by
one of the low speed DACs.

> 2. Or is it just the AD9862 PGA before the ADCs
> 3. The gain bar/parameter varies over 0-90, what does this represent?

Roughly the gain in dB relative to an unspecified point.

> 4. When you increase the gain from 0 till 30 or abouts there is no change in
> the noise floor? why is that? 

Not sure.

> If you have any docs that I can go through to understand the gain
> characteristic, please.

The code that controls the two parts of the gain setting can be found in

  db_flexrf.cc, flexrf_base_rx::set_gain

You might want to add a couple of printfs to that code to see what's
going on.

Eric